Motor vehicles are known which can be shifted from rear-wheel drive to four-wheel drive, for example, and in which the drives of the two axles can be rigidly coupled to each other by locking the associated differential. In addition, one or two differential locks may be provided for the rigid coupling of the wheel drives of one axle.
Moreover, anti-lock braking systems for motor vehicles are known which, for the control of the wheel slip, form a reference value whose curve optimally approximates that of the vehicle speed. In such system this reference value is formed by the use of different gradients.
The formation of the reference value is particularly difficult in the case of vehicles with four-wheel drive, and especially when, in addition, a central lock is engaged.